ON STYLOCHUS PELAGICUS. 03 



(nine fathoms) Antedon at Cape York and in a Holothuvian 

 found in 1975 fathoms near the Antarctic Sea. No doubt in 

 many instances in the case of deep-sea possessors of these 

 pigments, the pigments from being in the dark never exercise 

 their peculiar complex action on light during the whole life 

 of the animal, but remain in darkness, never showing their 

 colour, as does haemoglobin in so many animals. 



On Stylochus Pelaoicis, a neiv Species of Pelagic Pla- 

 NARiAN, with notes on other Pelagic Species, on the 

 Larval Forms of Thysanzoon, and of a Gymnoso- 

 MATOUS Pteropod. By H. N. Moseley, Fellow of 

 Exeter College, Oxford, Naturalist to the Challenger 

 Expedition. (With Plate III.) 



Stylochus pelagicus, a new Pelagic Planarian. 

 Darwin, in 'Ann. and Mag. Nat. Hist.,' xiv, 1844, p. 241, 

 251, pi. V, fig. 1, described and figured a Planarian, which 

 he found living free on the surface of the ocean, in lat. 5° 

 S., long. 33° W. He named this Planarian P/awa?'ia Oceanica. 

 The Planarian is referred to the genus Eurylepta Hempa. and 

 Ehrenberg, by Diesing, ' Syst. Helminthum,^ vol. 1, p. 211, 

 since it agrees Avith the characters of that genus, having a 

 distinct head Avith frontal tentacles. Two oceanic species of 

 Stylochus,^ S. Mertensi and S. pelhicidus (Diesing), were 

 described by Mertens, Mem. de I'Acad. Imp. des Sciences de 

 St. Petersburg, 6 ser. sci. ' Math. Phys. et Nat.' II, 13 tab. 

 I, figs. 4-6. Stylochus Mertensi inhabits the seaweed of the 

 Sargasso sea. It was found by Mertens in the Atlantic 

 between lat. 21°— 35° N., and long. 36°— 38°W. The species 

 was found by us in the Challenger in abundance on Sar- 

 gassum bacciferum, wherever we gathered the weed for 

 examination. Like the crabs Lupea and Nautilograpsus, 

 Scyllsea pelagica, the little fish Antennarius and almost all the 

 inhabitants of the gulf weed, it has a protective resemblance 

 in colour to the seaweed. With S. Mertensi occurred a 

 second species of Stylochus,^\h^.c\].^\K's> colourless and pellucid, 

 and which, doubtless, was Stylochus pellucidus. In it a 

 series of eyespots occur on the tentacles disposed in a single 

 row reaching from the base to the top anteriorly. 



Some notes Avere made on the anatomy of both tliese 

 Planarians in the fresh state, and specimens were preserved 

 for further examination, but the bottle containing them 



1 = Gnesioceros pellucidus and Mertensi Diesing Revision der turbel- 

 larien, ' Sitz. Acad. Wiss.,' Wien, 1861. 



